1. Field of the Invention
The present invention relates to a detecting device, more particularly to a position detecting device.
2. Description of the Related Art
Referring to FIGS. 1 and 2, U.S. Pat. No. 7,176,907 Taiwanese Patent No. I304559 discloses a conventional passive-type digital tablet pointing system that includes a digital tablet 1 and a wireless pointing device 2 (e.g., a digital stylus).
The wireless pointing device 2 includes a variable inductor 21, two capacitors 22, 23, and a switch 24, which, in combination, correspond to a resonance frequency. The variable inductor 21 has an inductance value that is in a negative relation to a contact pressure between the wireless pointing device 2 and the digital tablet 1. When the wireless pointing device 2 and the digital tablet 1 are in contact with each other, the inductance value of the variable inductor 21 decreases as the contact pressure between the wireless pointing device 2 and the digital tablet 1 increases, which consequently increases the resonance frequency of the wireless pointing device 2. When the switch 24 enters a conductive state, the capacitor 23 will cause the resonance frequency to decrease. The wireless pointing device 2 stores energy upon receipt of an excitation signal having the resonance frequency, and subsequently uses the energy thus stored to generate and transmit an oscillation signal having the resonance frequency.
The digital tablet 1 includes a plurality of first antennas 1/1-1/m arranged along a first direction, and a plurality of second antennas 2/1-2/n arranged along a second direction perpendicular to the first direction. The digital tablet 1 is configured to perform each of a full-region scan and a sub-region scan twice so as to obtain information corresponding to position (i.e., horizontal and vertical coordinate components) of the wireless pointing device 2 relative to the digital tablet 1, and information corresponding to operational states (e.g., the contact pressure between the wireless pointing device 2 and the digital tablet 1, and whether the switch 24 is in the conductive state) of the wireless pointing device 2. The digital tablet 1 detects the operation states of the wireless pointing device 2 based on frequency of the oscillation signals received by the digital tablet 1.
However, the aforesaid conventional passive-type digital tablet pointing system has several drawbacks.
First of all, since the excitation and oscillation signals have the same resonance frequency, the wireless pointing device 2 is unable to receive and transmit signals simultaneously, and hence regular refreshing of the position of the wireless pointing device 2 is relatively time-consuming.
Secondly, the digital tablet 1 must perform a full-region scan and a subsequent sub-region scan for each of the first and second directions so as to obtain the horizontal and vertical coordinate components, which is relatively complex and time-consuming.
Thirdly, like the wireless pointing device 2, the digital tablet 1 is unable to receive and transmit signals simultaneously. Moreover, since the signals transmitted and received by the digital tablet 1 have the same frequency, the digital tablet 1 must perform signal suppression while transmitting each signal so as to avoid receiving its own signal.
Lastly, since the antennas of the digital tablet 1 are substantially non-uniform in terms of distributed capacitance and impedance matching, the excitation signals transmitted by the digital tablet 1 have substantially different oscillation amplitudes. As a result, oscillation signals generated and transmitted by the wireless pointing device 2 upon receipt of the excitation signals have substantially different oscillation amplitudes, such that the digital tablet 1 must perform a relatively complex method of coordinate calculation.